Three volcanoes on Jupiter's moon Io erupted in a two-week spasm of violence last year, and UC Berkeley astronomers who watched them are wondering whether such outbursts could be far more common than scientists have thought.

The eruptions that spread lava over the Jovian moon could offer clues to the powerful volcanic forces that shaped the surfaces of planets in the inner solar system like Earth and its moon billions of years ago, the scientists say.

"I was just blown away when I saw that third eruption," said UC Berkeley astronomer Imke de Pater as she recalled the events she viewed through the powerful Keck telescope atop Mauna Kea in Hawaii a year ago.

'Something incredible'

"I realized that something incredible must be happening," de Pater said, "and it was telling me that there must be many more eruptions than we thought, and that if we could watch Io more often we might find out what's really happening on that moon - perhaps (learning) about Jupiter's influence on Io's deep mantle or even closer to its surface."

Astronomers typically expect to see only one huge volcanic outburst on Io every year or two, and they are normally not nearly as bright as the three de Pater saw last year, she said in a phone interview from Hawaii.

The temperature in Io's interior is thought to be about 2,600 degrees Fahrenheit, de Pater said, but the blistering heat could reach more than 3,000 degrees if the volcanoes are erupting more often than astronomers have thought, she said.

Powerful gravity

Those temperatures would be due to "tidal heating," caused by stresses on Io's crust from Jupiter's powerful gravity, de Pater said.

One of de Pater's colleagues is Katherine de Kleer, 27, her third-year graduate student who was also in Hawaii last August.

"I was able to watch that third eruption slowly decay," de Kleer said Wednesday as she continued observing the Jovian moon's surface, part of a year-long project studying Io.

Although it is just one of 67 known Jovian moons, Io holds a special place in Earth's history: It was one of the four satellites that Galileo discovered with his telescope 500 years ago.

As he watched Io and the other moons - Europa, Ganymede and Callisto - circling Jupiter in regular orbits, Galileo determined that the Earth could not be the center of all the stars in the universe, as the Vatican had long decreed.

Galileo was right

His public denial of church teaching led the Inquisition to convict Galileo of heresy - but his discovery ultimately led all astronomers to accept that the sun, not the Earth, is the center of all the planetary orbits.

Ashley Davies, a volcanologist at NASA's Jet Propulsion Laboratory and de Pater's longtime colleague, said the eruptions last year were similar to past events that spewed lava over hundreds of square miles of Io's surface.

"We are using Io as a volcanic laboratory where we can look back into the past of the terrestrial planets to get a better understanding of how such large eruptions took place, and how fast and how long they lasted," Davies said in a statement.

The eruptions that the astronomers watched were truly immense. The brightest, in a volcanic caldera called Rarog Patera, created a lava flow 30 feet thick covering 50 square miles of Io's surface. It was close to another caldera called Heno Patera, which spread lava over 120 square miles. The third volcano that erupted stands in a caldera called Loki.

De Pater and her colleagues will be publishing reports on Io's eruptions in the astronomy journal Icarus.